1. Field of the Invention
The invention concerns a microwave transmit or receive antenna. It is more particularly concerned with a flat annular microstrip resonant antenna.
2. Description of the Prior Art
Antennas of the above type are compact and lightweight. They are therefore used in vehicular applications, in particular in spacecraft and satellites.
There is often a need, in particular in space applications, for omnidirectional antennas, i.e. antennas that can send or receive within a large solid angle.
However, it has been found that the requirement for omnidirectionality is difficult to reconcile with the need to conserve the purity of the polarization of the electromagnetic waves transmitted or received.
In particular, when the wave to be transmitted (or received) must have circular polarization it is necessary to conserve an ellipticity close to 1 in all transmission (or reception) directions. This constraint is not easy to comply with in the case of plane antennas.
The invention aims to provide an annular resonant antenna of minimal overall size and maximal angular coverage within which coverage the purity of polarization is preserved.